Using the GNU Privacy Guard: Howto Create a Server Cert

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### 8.1 Creating a TLS server certificate

Here is a brief run up on how to create a server certificate. It has actually been done this way to get a certificate from CAcert to be used on a real server. It has only been tested with this CA, but there shouldn’t be any problem to run this against any other CA.

Before you start, make sure that gpg-agent is running. As there is no need for a configuration file, you may simply enter:

      $ gpgsm-gencert.sh >a.p10
      Key type
       [1] RSA
       [2] Existing key
       [3] Direct from card
      Your selection: 1
      You selected: RSA

I opted for creating a new RSA key. The other option is to use an already existing key, by selecting `2` and entering the so-called keygrip. Running the command ‘`gpgsm --dump-secret-key USERID`’ shows you this keygrip. Using `3` offers another menu to create a certificate directly from a smart card based key.

Let’s continue:

      Key length
       [1] 1024
       [2] 2048
      Your selection: 1
      You selected: 1024

The script offers two common key sizes. With the current setup of CAcert, it does not make much sense to use a 2k key; their policies need to be revised anyway (a CA root key valid for 30 years is not really serious).

      Key usage
       [1] sign, encrypt
       [2] sign
       [3] encrypt
      Your selection: 1
      You selected: sign, encrypt

We want to sign and encrypt using this key. This is just a suggestion and the CA may actually assign other key capabilities.

Now for some real data:

      Name (DN)
      > CN=kerckhoffs.g10code.com

This is the most important value for a server certificate. Enter here the canonical name of your server machine. You may add other virtual server names later.

      E-Mail addresses (end with an empty line)
      >

We don’t need email addresses in a server certificate and CAcert would anyway ignore such a request. Thus just hit enter.

If you want to create a client certificate for email encryption, this would be the place to enter your mail address (e.g. joe@example.org). You may enter as many addresses as you like, however the CA may not accept them all or reject the entire request.

      DNS Names (optional; end with an empty line)
      > www.g10code.com
      DNS Names (optional; end with an empty line)
      > ftp.g10code.com
      DNS Names (optional; end with an empty line)
      >

Here I entered the names of the servers which actually run on the machine given in the DN above. The browser will accept a certificate for any of these names. As usual the CA must approve all of these names.

      URIs (optional; end with an empty line)
      >

It is possible to insert arbitrary URIs into a certificate; for a server certificate this does not make sense.

We have now entered all required information and `gpgsm` will display what it has gathered and ask whether to create the certificate request:

      Parameters for certificate request to create:
           1	Key-Type: RSA
           2	Key-Length: 1024
           3	Key-Usage: sign, encrypt
           4	Name-DN: CN=kerckhoffs.g10code.com
           5	Name-DNS: www.g10code.com
           6	Name-DNS: ftp.g10code.com

      Really create such a CSR?
       [1] yes
       [2] no
      Your selection: 1
      You selected: yes

`gpgsm` will now start working on creating the request. As this includes the creation of an RSA key it may take a while. During this time you will be asked 3 times for a passphrase to protect the created private key on your system. A pop up window will appear to ask for it. The first two prompts are for the new passphrase and for re-entering it; the third one is required to actually create the certificate signing request.

When it is ready, you should see the final notice:

      gpgsm: certificate request created

Now, you may look at the created request:

      $ cat a.p10
      -----BEGIN CERTIFICATE REQUEST-----
      MIIBnzCCAQgCAQAwITEfMB0GA1UEAxMWa2VyY2tob2Zmcy5nMTBjb2RlLmNvbTCB
      nzANBgkqhkiG9w0BAQEFAAOBjQAwgYkCgYEA5h+uKRenpvbe+BnMY6siPO50LVyg
      HtB7kr+YISlPJ5JAFO12yQFz9Y0sBLHbjR+V+TOawwP1dZhGjlgnEBkMdWKuEBlS
      wFTALLX78GAyvAYAmPqSPDEYXkMECyUXVX/bbGI1bY8Y2OGy4w4D+v7e+xD2NBkm
      Bj5cNy+YMbGVldECAwEAAaA+MDwGCSqGSIb3DQEJDjEvMC0wKwYDVR0RBCQwIoIP
      d3d3LmcxMGNvZGUuY29tgg9mdHAuZzEwY29kZS5jb20wDQYJKoZIhvcNAQEFBQAD
      gYEAzBRIi8KTfKyebOlMtDN6oDYBOv+r9A4w3u/Z1ikjffaiN1Bmd2o9Ez9KXKHA
      IezLeSEA/rGUPN5Ur5qIJnRNQ8xrS+iLftr8msWQSZppVnA/vnqMrtqBUpitqAr0
      eYBmt1Uem2Y3UFABrKPglv2xzgGkrKX6AqmFoOnJWQ0QcTw=
      -----END CERTIFICATE REQUEST-----
      $

You may now proceed by logging into your account at the CAcert website, choose `Server Certificates - New`, check `sign by class 3 root certificate`, paste the above request block into the text field and click on `Submit`.

If everything works out fine, a certificate will be shown. Now run

    $ gpgsm --import

and paste the certificate from the CAcert page into your terminal followed by a Ctrl-D

      -----BEGIN CERTIFICATE-----
      MIIEIjCCAgqgAwIBAgIBTDANBgkqhkiG9w0BAQQFADBUMRQwEgYDVQQKEwtDQWNl
      cnQgSW5jLjEeMBwGA1UECxMVaHR0cDovL3d3dy5DQWNlcnQub3JnMRwwGgYDVQQD
      ExNDQWNlcnQgQ2xhc3MgMyBSb290MB4XDTA1MTAyODE2MjA1MVoXDTA3MTAyODE2
      MjA1MVowITEfMB0GA1UEAxMWa2VyY2tob2Zmcy5nMTBjb2RlLmNvbTCBnzANBgkq
      hkiG9w0BAQEFAAOBjQAwgYkCgYEA5h+uKRenpvbe+BnMY6siPO50LVygHtB7kr+Y
      ISlPJ5JAFO12yQFz9Y0sBLHbjR+V+TOawwP1dZhGjlgnEBkMdWKuEBlSwFTALLX7
      8GAyvAYAmPqSPDEYXkMECyUXVX/bbGI1bY8Y2OGy4w4D+v7e+xD2NBkmBj5cNy+Y
      MbGVldECAwEAAaOBtTCBsjAMBgNVHRMBAf8EAjAAMDQGA1UdJQQtMCsGCCsGAQUF
      BwMCBggrBgEFBQcDAQYJYIZIAYb4QgQBBgorBgEEAYI3CgMDMAsGA1UdDwQEAwIF
      oDAyBggrBgEFBQcBAQQmMCQwIgYIKwYBBQUHMAGGFmh0dHA6Ly9vY3NwLmNhY2Vy
      dC5vcmcwKwYDVR0RBCQwIoIPd3d3LmcxMGNvZGUuY29tgg9mdHAuZzEwY29kZS5j
      b20wDQYJKoZIhvcNAQEEBQADggIBAAj5XAHCtzQR8PV6PkQBgZqUCbcfxGO/ZIp9
      aIT6J2z0Jo1OZI6KmConbqnZG9WyDlV5P7msQXW/Z9nBfoj4KSmNR8G/wtb8ClJn
      W8s75+K3ZLq1UgEyxBDrS7GjtbVaj7gsfZsuiQzxmk9lbl1gbkpJ3VEMjwVCTMlM
      fpjp8etyPhUZqOZaoKVaq//KTOsjhPMwz7TcfOkHvXketPrWTcefJQU7NKLH16D3
      mZAwnBxp3P51H6E6VG8AoJO8xCBuVwsbXKEf/FW+tmKG9pog6CaZQ9WibROTtnKj
      NJjSBsrUk5C+JowO/EyZRGm6R1tlok8iFXj+2aimyeBqDcxozNmFgh9F3S5u0wK0
      6cfYgkPVMHxgwV3f3Qh+tJkgLExN7KfO9hvpZqAh+CLQtxVmvpxEVEXKR6nwBI5U
      BaseulvVy3wUfg2daPkG17kDDBzQlsWC0BRF8anH+FWSrvseC3nS0a9g3sXF1Ic3
      gIqeAMhkant1Ac3RR6YCWtJKr2rcQNdDAxXK35/gUSQNCi9dclEzoOgjziuA1Mha
      94jYcvGKcwThn0iITVS5hOsCfaySBLxTzfIruLbPxXlpWuCW/6I/7YyivppKgEZU
      rUTFlNElRXCwIl0YcJkIaYYqWf7+A/aqYJCi8+51usZwMy3Jsq3hJ6MA3h1BgwZs
      Rtct3tIX
      -----END CERTIFICATE-----
      gpgsm: issuer certificate (#/CN=CAcert Class 3 Ro[...]) not found
      gpgsm: certificate imported

      gpgsm: total number processed: 1
      gpgsm:               imported: 1

gpgsm tells you that it has imported the certificate. It is now associated with the key you used when creating the request. The root certificate has not been found, so you may want to import it from the CACert website.

To see the content of your certificate, you may now enter:

      $ gpgsm -K kerckhoffs.g10code.com
      /home/foo/.gnupg/pubring.kbx
      ---------------------------
      Serial number: 4C
             Issuer: /CN=CAcert Class 3 Root/OU=http:\x2f\x2fwww.[...]
            Subject: /CN=kerckhoffs.g10code.com
                aka: (dns-name www.g10code.com)
                aka: (dns-name ftp.g10code.com)
           validity: 2005-10-28 16:20:51 through 2007-10-28 16:20:51
           key type: 1024 bit RSA
          key usage: digitalSignature keyEncipherment
      ext key usage: clientAuth (suggested), serverAuth (suggested), [...]
        fingerprint: 0F:9C:27:B2:DA:05:5F:CB:33:19:D8:E9:65:B9:BD:4F:B1:98:CC:57

I used `-K` above because this will only list certificates for which a private key is available. To see more details, you may use `--dump-secret-keys` instead of `-K`.

To make actual use of the certificate you need to install it on your server. Server software usually expects a PKCS\#12 file with key and certificate. To create such a file, run:

      $ gpgsm --export-secret-key-p12 -a >kerckhoffs-cert.pem

You will be asked for the passphrase as well as for a new passphrase to be used to protect the PKCS\#12 file. The file now contains the certificate as well as the private key:

      $ cat kerckhoffs-cert.pem
      Issuer ...: /CN=CAcert Class 3 Root/OU=http:\x2f\x2fwww.CA[...]
      Serial ...: 4C
      Subject ..: /CN=kerckhoffs.g10code.com
          aka ..: (dns-name www.g10code.com)
          aka ..: (dns-name ftp.g10code.com)

      -----BEGIN PKCS12-----
      MIIHlwIBAzCCB5AGCSqGSIb37QdHAaCCB4EEggd9MIIHeTk1BJ8GCSqGSIb3DQEu
      [...many more lines...]
      -----END PKCS12-----
      $

Copy this file in a secure way to the server, install it there and delete the file then. You may export the file again at any time as long as it is available in GnuPG’s private key database.

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